The present invention relates to an automatic transmission which is mounted on, for example, a vehicle. More particularly, the present invention relates to an automatic transmission having two clutches provided at different radial positions so as to axially overlap each other.
In recent years, a multi-speed automatic transmission, such as an automatic transmission with eight forward speeds, has been increasingly developed as an automatic transmission to be mounted on a vehicle, from the standpoint of improving fuel consumption and emission of the vehicle. Moreover, many components, such as clutches, are required to be compactly arranged, from the standpoint of vehicle mountability.
In an automatic transmission of a related art, two clutches, having one of input and output members in common and the other of the input and output members not in common, are disposed at different radial positions so as to axially overlap each other, in order to make the automatic transmission compact, especially in the axial direction (see, for example, Japanese Patent Application Publication No. JP-A-H07-269665). In these two clutches, multiple friction plates, a hydraulic servo for engaging and disengaging the friction plates, and a cancel oil chamber for cancelling a centrifugal oil pressure of a hydraulic oil pressure chamber of a piston are disposed so as to axially overlap each other.
An oil is directly supplied to the cancel oil chamber on the inner diameter side of the above two cancel oil chambers through an oil gallery formed in a boss portion of a clutch drum, and the oil in the cancel oil chamber on the inner diameter side is supplied to the cancel oil chamber on the outer diameter side through the piston and an oil gallery formed in the clutch drum of the clutch on the inner diameter side.